1. Field of the Invention
This invention relates to multi-layer flexible packaging materials and in particular to a material which includes a three component, co-extruded layer which imparts to the material superior properties in comparison with prior art materials.
2. Description of the Prior Art
The development of improved flexible packaging materials has been a continuing problem in the packaging and container art. Over the years, numerous flexible laminates have been proposed. For example, Lacy, U.S. Pat. No. 3,480,464, discloses a wrapping or packaging material composed of a paper layer, a first polyolefin layer, a metal layer and a second polyolefin layer. The metal layer is vacuum deposited on the first polyolefin layer. The preferred polyolefin is polyethylene.
Similarly, Gilbert et al, U.S. Pat. No. 4,239,639, shows a multi-layer laminate which can include a paper layer, a foil layer, a Surlyn layer and a polyethylene layer. The laminates can be co-extruded or adhesive mounted. This patent requires an outer layer selected from the group consisting of oriented polypropylene, polyester, cellophane or mixtures thereof.
Stillman, U.S. Pat. No. 4,096,309, shows a laminate which includes paper, polyethylene, metal, and a heatsealable polyolefin. This patent requires a layer consisting of a nonwoven sheet of spun-bonded polymeric filaments.
Japanese Patent Abstract No. 52-012311 discloses a three layer laminate comprising a base paper laminated to a low density polyethylene film which in turn is metallized with aluminum. Peer, Jr., U.S. Pat. No. 4,254,173, shows a similar paper/polyethylene/vacuum deposited metal laminate.
French Patent Abstract No. 2,454,904 discloses a coextruded three layer film having an inner layer of high density polyethylene and two outer layers which can comprise, among other things, an ionomer resin, e.g., Surlyn.
Cook, U.S. Pat. No. 4,188,441, shows a co-extrusion of high density polyethylene and a blend of an ionomer with a copolymer, such as a copolymer of ethylene and ethyl methacrylate.
Rebholz U.S. Pat. No. 4,387,126 discloses a laminate which can comprise, from outside in, paper, polyolefin adhesive, metal foil and a three layer coextrudate comprising a first layer of ethylene-methyl acrylate, a middle layer of polyester and a third layer of ethylenemethyl acrylate.
In general, materials for use in manufacturing packages or containers must simultaneously satisfy a plurality of demanding conditions. For example, such material must be able to withstand rough and abusive treatment. Also, in many cases, the material must be able to endure prolonged exposure to corrosive substances which are placed in containers made from the material. Further, the material should provide an impervious barrier so as to isolate substances within containers made from the material from the outside atmosphere. In many cases, it is also desirable that the flexible material be such that it can be heat sealed to itself. In addition to the foregoing requirements, the material must retain its flexibility and must not exhibit laminate separation during use.